iphone - respondsToSelector 总是失败

Question

我正在编写自己的 gridview 实现(基于 tableview 模式)。我遵循了类似于 TableView 的数据源模型，但是当我检查数据源是否响应消息时，调用总是失败。

我已经尝试放置断点并在执行后，我什至尝试错过对 respondsToSelector 的调用。我尝试的任何事情似乎都不起作用。我在这里错过了什么？提前致谢

GridView.h

    ...
    @protocol GridViewDataSource 
    - (NSInteger) numberOfRowsForGridView:(GridView *)gridView;
    - (NSInteger) numberOfColumnsForGridView:(GridView *)gridView;

    - (GridViewCell *) cellForRow:(NSInteger) row column:(NSInteger )column;
    @end 

GridView.m

    ...
    #pragma mark datasource methods
    -(NSInteger)numberOfRowsForGridView
    {
        if( [dataSource respondsToSelector:@selector(numberOfRowsForGridView:)] )
           return [dataSource numberOfRowsForGridView:self];
       // NSLog(@"Failed, dataSource does not implement properly");
        return 0;
    }

    -(NSInteger)numberOfColumnsForGridView
    {
        if( [dataSource respondsToSelector:@selector(numberOfColumnsForGridView:)] )
            return [dataSource numberOfColumnsForGridView:self];
        return 0;
    }

    -(GridViewCell *)cellForRow:(NSInteger)row column:(NSInteger)column
    {
        if( [dataSource respondsToSelector:@selector(cellForRow:column:)])
            return [dataSource cellForRow:row column:column];
        return nil;
    }

GridViewAppDelegate.h

    ...
    @interface GridViewAppDelegate : NSObject <UIApplicationDelegate, GridViewDataSource>
    ...

GridViewAppDelegate.m

    #pragma mark datasource methods
    -(NSInteger)numberOfRowsForGridView:(GridView *)gridView
    {
        return 1;
    }

    -(NSInteger)numberOfColumnsForGridView:(GridView *)gridView
    {
        return 1;
    }

    -(GridViewCell *)cellForRow:(NSInteger)row column:(NSInteger)column
    {
        CGRect frame = [view bounds];


        GridViewCell *cell = [[GridViewCell alloc]initWithFrame:frame];
        return cell;
    }

Answer 1

您的 dataSource 对象是 nil 吗？

发送到 nil 的任何消息都将返回 NO bool 结果(数字为 0，对象也为 nil) .